1. Field of the Invention
This invention relates to a personal computer system having an extended unit for connecting the main body of the system to, for example, an extended memory board, and more particularly, to a computer system having an extended unit including a power supply dedicated thereto.
2. Description of the Related Art
In the field of personal computers, lap-top type computers which are compact, light, and portable are popular. Each of them has standard equipment comprising a system main body, and its peripheral devices such as a keyboard, a liquid crystal display, and a floppy disk. In these compact computers, however, it is not possible to have many standard functions or many input/output devices which enable the system to have various standard functions. For example, the system is not capable of communicating with another computer.
Some of the above-described compact computers are adapted to be connected to an extended unit which allows them to have functions other than standard ones. The extended unit has a slot (connector member) for connecting the system to an extended board incorporating a logic circuit, a memory circuit, etc. The extended unit includes a power source, independent of that of the host system, for driving the logic circuit, memory circuit, etc., in the extended board.
Some personal computers have a resume function of resuming, upon turn-on of the system, the program interrupted by turning off the system. In these computers, when the system, having the resume function, is turned off in a state where the resume mode is set in the setup menu of the system, data registered in various registers and required for effecting the program are stored in a memory (RAM) backed up by a battery dedicated thereto. Then, when the system is turned on again, the stored data are returned to the registers.
In the above computers, there is a case where an extended board set in the extended unit is connected to the system assuming resume mode and storing the data of registers in a memory. In this case, if the system is turned on after the extended unit is connected thereto, and the data stored in the memory are returned to the registers, the data may be damaged due to the connection of the extended unit to the system. This is because the circuits incorporated in the extended board are being driven by the power source included in the extended unit, and hence are communicable with the system. Hence, the data may be changed from that stored immediately before the turn-off of the system, data exchange may be carried out between the system and extended unit without effecting resume mode processing.